1. Field of the Invention
The present invention relates to electronic control devices to be disposed in the engine room of an automobile, and particularly to a casing for the electronic control device which is improved in its water-proofing structure.
2. Related Art
An ECU (Engine Control Unit) being developed is shown in FIGS. 13-18.
First of all, a casing 4 of an ECU 1 is constructed, as shown in FIG. 13, to include: a casing body 5 having a shape of a rectangular container; and a cover 8 for closing the opening 51 in the upper face portion of the casing body 5. A printed circuit board 2 is mounted in the casing body 5 by means of screws 21. Moreover, a connector 3 is mounted on the right-hand end portion of the printed circuit board 2. In the right-hand sidewall portion 55 of the casing body 5, there is formed a connector opening 56 which communicates with the opening 51 for fitting the connector 3.
At the open edge portion of the casing body 5, as also shown in FIG. 14, there is formed a flange portion 58 having an upper face, in which there is formed a groove portion 59 for fitting a liquid sealing material 9 therein. Here, the groove portion 59 is omitted from FIG. 13.
In this construction, the liquid sealing material 9 is applied to the casing body 5 and the connector 3, as hatched in FIG. 13. Moreover, the printed circuit board 2 is mounted in the casing body 5 by means of the screws, and the cover 8 is mounted in the opening 56 (or on its flange portion 58) of the casing body 5 by means of the screws. Then, the flange portion 82 of the cover 8 and the flange portion 58 of the casing body 5 are sealed up by the liquid sealing material 9, as shown in FIG. 14. Although not shown, moreover, the upper face portion of the connector 3 and the flange portion 82 of the cover 8, the lower face portion of the connector 3 and the bottom face portion of the connector opening 56, and the two outer side portions 33 and 34 of the connector 3 and the two inner side portions 62 and 63 of the connector opening 56 are likewise sealed up by the liquid sealing material 9. Thus, the casing 4 is constructed to have a sufficient water-proofing performance.
In this construction of the prior art, the cover 8 is die-cast of aluminum to have a considerable thickness. Therefore, the construction has a problem that the cover 8 has a high production cost and a large weight. In order to solve this problem, we have conceived a construction in which the cover 8 is formed by pressing a thin steel sheet, for example.
However, the cover 8 of the thin steel sheet is made thin and short of a rigidity (or strength) in its entirety and is troubled by the warpage or distortion as a whole. If the cover 8 thus warps or is distorted, moreover, its flange portion 82 is deteriorated in its flatness, as shown in FIG. 15, so that the liquid sealing material 9 applied to the flange portion 58 of the casing body 5 partially fails to contact with the flange portion 82 of the cover 8 thereby to cause a defect that their sealing is incomplete.
In the case of an assembly in normal positions, more specifically, clearances of individually proper distances are formed between the two outer side portions 33 and 34 of the connector 3 and the two inner side portions 62 and 63 of the connector opening 56, as shown in FIG. 16. If the liquid sealing material 9 is fitted in these proper clearances, moreover, the sufficient sealing performance can be achieved.
When the connector 3 is so assembled as is located at a position displaced transversely from the normal position in the connector opening 56, on the contrary, one clearance is considerably reduced, as shown in FIG. 17. With a small clearance, if any, the liquid sealing material 9 does exist in the clearance so that the sealing performance can be retained. As shown in FIG. 17, however, the small clearance causes a trouble that the overflow of the liquid sealing material 9 increases.
When the assembly is made such that the connector 3 is more displaced transversely from the normal position in the connector opening 56, on the other hand, one side portion 34 (or 33) of the connector 3 comes into contact with (or into abutment against) one inner side portion 63 (or 62) of the connector opening 56, as shown in FIG. 18. In this case, the liquid sealing material 9 is scraped off to raise a problem the sealing performance is lost.
This invention has been conceived in view of the background thus far described and its first object is to provide a casing for an electronic control device which can prevent the cover from warping or from being distorted thereby to seal up the cover and the casing body reliably, although the cover is made of a thin sheet.
A second object of the invention is to provide a casing for an electronic control device, which can retain a clearance reliably between the two side portions of a connector and the two inner side portions of a connector opening thereby to retain a sufficient sealing performance, even with a low accuracy in the connector assembling position.
According to a first aspect of the invention, the opening of the upper face portion of the casing body for housing the electronic circuit unit is closed by the cover made of a thin sheet, and the groove portion formed in the open edge portion of the casing body is charged with the liquid sealing material for sealing the open edge portion of the casing body and the peripheral edge portion of the cover. Moreover, the ridge portion having a generally U-shaped section is so formed on the peripheral edge portion of the cover as to be fitted in the groove portion of the casing body. According to this construction, the ridge portion having the generally U-shaped section is formed on the peripheral edge portion of the cover so that the cover can be prevented from warping or from being distorted although it is made of the thin sheet. As a result, the cover and the casing body can be reliably sealed up. On the other hand, the ridge portion of the peripheral edge portion of the cover contacts with the liquid sealing material so that the length of contact with the liquid sealing material, i.e., the sealing length can be enlarged to enhance the sealing performance. Moreover, the amount of the liquid sealing material to fill up can be reduced by an amount corresponding to the sectional area of the ridge portion of the peripheral edge portion of the cover.
According to a second aspect of the invention, the electronic circuit unit is made of the printed circuit board, and the connector opening is so formed in the sidewall portion of the casing body as to communicate with the opening and to fit the connector at one end portion of the printed circuit board. Moreover, there is formed in the upper face portion of the connector the groove portion to be charged with the liquid sealing material. According to this construction, the printed circuit board can be assembled from the upper side in the casing body to improve the assembling workability. While making this upside assembly possible, moreover, it is possible to seal up the cover and the casing body, the cover and the connector, and the connector and the casing body reliably.
According to a third aspect of the invention, when the cover for closing the opening of the casing body is not made of a thin sheet, the wall portion is formed to rise from the open edge portion of the casing body on the outer side of the groove portion. According to this construction, the liquid sealing material can be prevented from overflowing by the wall portion when it is caused by the dispersion of its charge to overflow to the outside from between the open edge portion of the casing body and the peripheral edge portion of the cover.
According to a fourth aspect of the invention, the connector can be positioned by the positioning portion which is disposed on the two inner side portions of the connector opening or on the two outer side portions of the connector, thereby to retain a predetermined clearance between the inner side portions of the connector opening and the outer side portions of the connector. Even with a low accuracy of the assembled position of the connector, therefore, the clearance can be reliably retained between the two side portions of the connector and the two inner side portions of the connector opening of the casing body. As a result, a sufficient sealing performance can be achieved by fitting the liquid sealing material in that clearance.